Tumor necrosis factor-alpha (TNF-alpha) is a pro-inflammatory cytokine that has pleiotropic effects on a wide variety of tissues. The role of TNF-alpha in insulin-dependent diabetes mellitus (IDDM) has been a controversial issue. Previous studies have shown that in vitro, TNF- alpha in combination with other cytokines such as IL-1 is cytotoxic to pancreatic beta cells while administration of TNF-alpha in vivo in adult non-obese diabetic (NOD) mice can prevent diabetes. Recently, it has been shown that TNF-alpha is produced very early during thymic development and that administration of anti-TNF-alpha antibody can block normal thymic development in mice. Interestingly, our most recent study has demonstrated that administration of TNF-alpha in newborn NOD mice, in contrast to the result obtained with adult mice, accelerates disease onset while anti-TNF-alpha treatment inhibits insulitis and completely prevents diabetes. These data indicate that TNF-alpha may play a critical role in lymphocyte development and particularly in the generation of autoimmunity to pancreatic beta cells. Our proposed study will focus on the cellular and molecular mechanisms by which TNF-alpha can effect both the development of immature lymphocytes in the thymus and the function of mature T helper cells and effector cytotoxic lymphocytes. The approaches to be used will include: (1) treatment of newborn NOD mice with TNF-alpha or monoclonal anti-TNF-alpha antibody; (2) examination of TNF-alpha's effect on normal lymphocyte development, and on negative selection; (3) determination of the role of TNF-alpha in the regulation of autoantigen-specific Th1 vs. Th2 responses; (4) measurement of TNF- alpha mediated specific cytotoxic activity specific for pancreatic beta cells; and (4) assessment of the potential effect of TNF-alpha on lymphocyte homing to the pancreatic islets. These studies may lead to a further understanding of the immunopathogenesis of IDDM. A corollary of this work is the possible development of novel approaches for cytokine-based immunotherapy of IDDM.